Only two months ago, the race for nominations to Alexandria's two seates in the Virginia House of Delegates seemed fairly routine. The incumbents, a Democrat and a Republican, were expected to seek reelection and there was a strong possibility that neither party would hold a primary.

Now, three Democrats are competing for the two nominations in next Tuesday's primary, while the Republicans narrowly avoided a primary battle when one of three GOP candidates dropped out at the last minute.

Heavy campaigning began when Democratic Del. Richard R. G. Hobson, a two-term veteran of the legislature, and Republican Del. Gary R. Myers, who had served one two-year term, decided to retire from the $5,800-a-year jobs, citing personal reasons.

The Republicans chose their nominees at a meeting of the GOP Central Committee last night.

The Republican nominees are David G. Speck, a former City Council candidate, and Betty McCann, a former Capitol Hill aide to Rep. Joel T. Broyhill (R) and Sen. William L. Scott (R).Michael E. Norris, Alexandria's sheriff, dropped out of the race.

Speck, 33, emphasized cost-cutting and government efficiency during his council campaign. McCann, 50, once an aide to Rep. Joel T. Broyhill (R-Va.) and Sen. William L. Scott (R-Va.), said she would press for property tax and divorce law reform, if elected, as well as passage of the Equal Rights Amendment.

Democratic voters at next Tuesday's primary will choose among Nancy Bennett, a political campaign adviser and consumer activist; Bernard S. Cohen, an environmentalist attorney and Joseph M. Guiffre, businessman.

Bennett, 34, has waged an outspoken campaign against rate practices of the Virginia Electric and Power Co. That undertaking is expected to help her with liberal voters who usually turn out in great numbers for primaries, according to several politicians.

Cohen, 45, said he would work to force oil companies to sell their retail gas stations "so the small capitalists can thrive in Virginia." Cohen, a former supporter of populist Democratic gubernatorial candidate Henry Howell has waged what he calls a "low key" campaign, relying primarily on word of mouth.

Guiffre, 45, a well-known AnheuserBusch beer distributor and former president of the Alexandria Chamber of Commerce, is campaigning against unfair taxes on food and real estate." He said he would try to abolish the 4 percent sales tax onfood and seek to control property taxes, which he says are "artificially" increased by inflation.

Bennett and Guiffre each expect to spend about $5,000 in the primary.Cohen said he expects to spend about $1,000.

Cohen and Guiffre have been endorsed by City Councilmen Donald C. Casey and Nelson E. Greene Sr. Greene is only the second black person to win a council seat since Reconstruction.

Incumbent Del. Elise B. Heinz, a Democrat, is running without Republican opposition for reelection to the House from the 23d district, which includes both Alexandria and Arlington. Independent candidates have until June 12 to file for any delegate race.

Although Alexandria Republicans will not hold a primary to choose their nominees for the House of Delegates, and a number of other offices, they will have a primary to pick a Commonwealth's Attorney nominee.

Republicans Barry Poretz and Ken Foran are in an apparently close race for the nomination to the prosecutor's job. Some politicians have speculated that a strong showing by Guiffre in the Democratic House primary could hurt Poretz' chances.

This is because both Guiffre and Poretz have waged similar campaigns, emphasizing their long ties to the city. Since voters must choose to cast either Democratic or Republican ballots, a strong showing for Guiffree in the Democratic balloting could pull voters away from the Republican primary where Poretz is running, according to one view.

Either Poretz or Foran will face incumbent Commonwealth's Attorney John E. Kloch, a Democrat, next November.

An estimated 3,500 of the 5,000 voters expected to got to the polls Tuesday will ask for Democratic ballots, according to voter registrar Stanford Hurst.

The city's 32 polling places will be open from the 6 a.m. to 7 p.m.